Electrochromism is a phenomenon where an oxidation-reduction reaction is reversibly caused to reversibly change a color by applying voltage. An electrochromic material exhibiting the electrochromism is typically formed between two facing electrodes, and an oxidation-reduction reaction of the electrochromic material is caused in a structure where a space between the electrodes is filled with an electrolyte layer capable of conducting ions. When a reduction reaction occurs adjacent to one of the two facing electrodes, an oxidation reaction, which is a reverse reaction of the reduction reaction, occurs adjacent to the other electrode.
When voltage is applied, coloring occurs at both the electrodes in a device using the electrochromic material, to thereby change a color or optical density.
In a case where a transparent display device is produced with an electrochromic display element using the electrochromic material, or a case where a device having a structure, in which three coloring layers of cyan (C), magenta (M), and yellow (Y) are laminated, is produced with the electrochromic display element, it is important that the electrochromic display element is composed of a material that can be in a state of colorless transparent. As the electrochromic material that can exhibit such a state, reported are viologen compounds and triaryl amine compounds exhibiting an electrochromic phenomenon where a neutral state is a transparent state and coloring occurs in a reduced state (see, for example, NPL 1).
However, coloring of the triaryl amine compounds disclosed in NPL 1 is from blue to cyan or green, and it is difficult to obtain stable coloring of yellow (Y) or magenta (M).